The demand for wireless telecommunication performance is increasing rapidly. People not only request for a higher speed communication, but also want to enjoy a wide and diverse coverage of services. Because of these demands, researchers have been looking for new technologies to improve the efficiency on communication. The efforts have been put to obtain a higher degree of spectral and energy efficiencies, and/or be able to flexibly adjust the combinations of the two. It is necessary to improve the flexibility and efficiency in systems used in the telecommunication.
It is believed that the technology of index modulation (“IM”) for multiple-input and multiple-out (“MIMO”) and multiple carriers are both of potential to be adopted in the next generation wireless communication systems. In the past few years, the IM related researches have gained more and more attention because of the theoretical advantages. In the context of IM, the indices of the resources in a considered communication system are used to convey additionally information bits. Thus, it facilitates the digital modulation scheme to achieve higher spectral and energy efficiencies.
The two state-of-the-art applications for IM are 1) spatial modulation (“SM”) and 2) orthogonal frequency division multiplexing with IM (“OFDM-IM”) schemes. In the respect of SM, the corresponding index modulated building blocks are the transmit antennas of a MIMO system. As to OFDM-IM, the corresponding index modulated building blocks are the subcarriers of an OFDM system.
The two above applications are problematic. The SM relies on combinations of antennas to carry out index modulation. However, it requires hardware components to switch the selected antennas on-and-off and consequently limits the processing speeds substantially. Further, SM is incompatible to OFDM-based communication systems because the antennas' switching would affect all of the subcarriers simultaneously. This incompatibility issue makes SM unfit for current communication systems. As for OFDM-IM, it does not efficiently exploit the degree-of-freedom which MIMO can provide.